The present invention relates to electrophotographic copying machines in general, and more particularly to improvements in copying machines wherein electrostatic images at the active face of a mobile printing base are developed with a liquid toner, i.e., with a developing agent wherein minute toner particles are distributed in a liquid suspension medium. Still more particularly, the invention relates to improvements in liquid toner developing apparatus wherein the active face of the printing base moves along and is substantially parallel to one side of a developing electrode while the electrostatic image on the active face is being contacted with liquid toner. Still more particularly, the invention relates to developing apparatus of the just outlined character wherein the developing electrode is preferably impermeable to liquid toner and the liquid toner fills the space between the electrode and the active face of the printing base.